预固化环氧树脂基复合材料自粘结性能研究

通过拉丝法测定了5228A环氧树脂在不同温度下的凝胶时间,选择了特定的预固化温度;在预固化温度下制备了不同预固化度的碳纤维增强环氧树脂基复合材料,采用DMA测试了预固化复合材料层板的玻璃化转变温度;采用自制粘接模具制备了复合材料自粘结接头,测试了复合材料接头的搭接剪切性能;采用光学显微镜观测了自粘结搭接结构和剪切断口形貌,分析了搭接结构对剪切强度的影响。结果表明:复合材料层板的预固化度<αgel时,接头的搭接剪切强度变化不大,当预固化度>αgel时,接头的搭接剪切强度降低幅度较大;剪切性能受搭接结构的完整性影响较大。     

环氧树脂基预浸料热固化特征温度和固化度研究

基于固化动力学理论和有限元分析方法,建立了树脂基预浸料热固化过程中温度场研究的数学模型,数值模拟了预浸料固化过程的温度和固化度变化特征,将数值计算结果与已有文献实验结果对比,验证了计算模型和计算方法的正确性.研究了升温速率、玻璃纤维等因素对环氧树脂体系固化反应特征温度以及固化时间的影响.结果表明,升温速率增加,固化反应放热峰Tp向高温方向移动,同时固化起始温度Ti和固化终止温度Tf也相应地向高温移动,固化过程中材料内温度梯度增大,内部热应力增大.但提高升温速率可缩短固化完成所需时间.玻璃纤维的加入使树脂基预浸料各项固化反应特征温度降低,达到固化起始温度的时间延长,但对完成固化时间的影响可忽略.     

湿法缠绕用次中温固化的环氧树脂配方

采用自制改性液态芳香胺制得一种低粘度次中温固化环氧树脂体系，通过不同升温速率下的固化过程DSC扫描，研究了该体系的固化反应动力学，并据其优化了体系的固化制度。结果表明，该体系的表观固化反应活化能为38．54kJ／mol，反应级数为0．84。固化度和FT—IR测试表明，体系可在90℃次中温环境中达到固化完全。体系综合性能优良，可满足复合材料湿法缠绕成型对高性能树脂基体的要求。     

不同化学结构环氧树脂电子束固化效果的分析

研究了化学结构对环氧树脂电子束辐射反应速率和辐射固化效果的影响。对于分子量相近的环氧树脂，反应速率大的环氧树脂体系最终达到的反应程度较高。酚醛型环氧树脂辐射反应活性高，固化后的高温模量及玻璃化转变温度高于双酚A型环氧树脂，但固化度沿辐射深度方向下降较快，脂环族环氧树脂的辐射反应活性小，在相同辐射条件下的固化效果差。缩水甘油胺结构的环氧树脂对于碘Wong盐引发的电子束辐射固化反应没有活性。     

增塑剂对预涂饰装饰纸性能及生产工艺的影响

通过考察几种增塑剂用于预涂饰装饰纸浸溃树脂的使用效果，探索聚丙烯酸酯作为氨基浸渍树脂增塑剂的可能性。研究增塑剂对浸渍树脂适用期的影响及对预涂饰装饰纸预固化度、柔韧性和耐潮性的影响。结果表明：聚丙烯酸酯能促进和参与氨基树脂的交联反应，提高预涂饰装饰纸的各种性能。当增塑剂的用量达到树脂量的50％以上时，即使不加固化剂，浸溃纸预固化度也可达到70％以上而满足工艺要求；当增塑剂为树脂量的40％～50％时，纸张的柔韧性明显提高，其弯曲半径达到3mm；当氨基树脂中加入的增塑剂量与树脂量相同时，浸渍纸吸湿率可降低30％左右，耐潮性明显增强。增塑剂也会缩短浸渍树脂的适用期，当增塑剂为树脂量的30％～50％时，适用期最短，加人抑制剂后方可满足生产工艺要求的适用期。     

DSC法测定环氧树脂固化反应温度和反应热

介绍了差示扫描量热法（DSC）测试环氧树脂固化反应温度和反应热的原理和试验条件，研究了升温速率和样品量对测定结果的影响，对试验方法的不确定度进行了分析和评定，并进行了应用试验。结果表明，该方法对环氧树脂及其预浸料实施有效的质量控制具有重要的意义。     

丙烯酸酯无皂水溶胶涂料热固化性能的研究

用红外光谱法和差热分析法研究了热固性丙烯酸酯无皂水溶胶与六甲氧基甲基三聚氰胺(HMMM)的固化过程。实验表明水溶胶的固化是分两步进行的,羟基和羧基与固化剂HMMM上的甲氧基在不同的温度区间交联固化,并且羟基的交联固化反应温度低于羧基的。同时,考察了固化剂用量对固化温度和固化度的影响。     

RTM工艺用室温可固化环氧树脂体系性能研究

选取了三种低黏度且可以室温固化的环氧树脂体系:QC350A/B,1564/HY3487,EV6620/HVC188,表征了树脂体系的流变性能、室温固化固化度及固化物弯曲性能。结果表明:三种环氧树脂体系在20~50℃有适于树脂传递模塑(RTM)工艺的低黏度操作平台;室温固化2周内固化度可达到90%,可以完成室温固化;室温固化21 d弯曲强度与高温后处理试样相当,弯曲弹性模量优于高温后处理试样,室温固化能够满足使用性能要求。     

热固性树脂半固化片树脂流动度研究

采用聚丁二烯、丙酮、陶瓷粉填料和其他助剂,制得胶液,用偶联剂处理过的玻璃布在胶液中浸渍后,在70℃干燥脱溶剂,在140℃继续烘烤10 min,得到半固化状态的预浸片。将浸渍片按固定的尺寸裁切后即得到所需的热固性树脂半固化片。对半固化片关键指标之一的树脂流动度的影响因素及调控方法进行了较为详细的讨论。结果表明,在良好界面改性的同时,当陶瓷粉配比中球角比越小、烘道温度越高时,半固化片的树脂流动度越低,相反则流动度越大,流动度调整范围可从0.7%到20.5%。通过对相关影响因子的合理调控,就能得到满足不同使用要求的半固化片,满足不同情况下多层板的设计加工要求。     

先进拉挤工艺下工字梁固化温度场的二维数值模拟

碳纤维增强复合材料在固化成型过程中,其温度与固化度的变化历程具有强耦合关系,以含有非线性内热源的瞬态热传导方程为基础,利用有限容积法编写了计算程序,研究了以T300/环氧预浸料为材料的某复合材料工字形地板梁在先进拉挤工艺下的温度、固化度的变化历程。结果表明:该工字形地板梁在厚度为5.9 mm时,固化过程中的温度场和固化度场基本可以认为是均匀的,其厚度不会对固化质量产生较大影响;当该工字梁的厚度达到11 mm时,制件最高温度比模具温度高出了10.7℃,这时制件厚度已对制件的固化质量产生较大影响。     

Fluorescence method for monitoring isothermal curing and shelf life of an epoxy–anhydride system

A fluorescence technique with seven fluorescent probes was applied to monitor the curing and shelf life of an epoxy resin. As isothermal curing proceeded, the fluorescence emission bands of the probes exhibited blue shifts because of microviscosity and micropolarity changes. An intensity ratio method was applied in which ratios of the lowest and highest intensity changes in the emission bands were used to determine the degree of isothermal curing. A smooth and, in some cases, a linear correlation was found between the fluorescence intensity ratio and the degree of cure. This method enables the degree of cure to be monitored and allows comparable results from different types of probes to be monitored during the same curing process. The fluorescence technique and the ratio method offer the possibility of monitoring the precuring and the shelf life of the epoxy polymer. The method can be used to compare the kinetics of various monomers and resin formulations under constant curing conditions. Thus, the method would be useful for developing new resin formulations and technologies and could be applied to a variety of commercial and industrial uses of epoxy resins. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2607–2615, 2001     

5%乙烯-醋酸乙烯共聚物复合低热水泥浆体的碳化促进养护

采用碳化养护方法促进5%乙烯-醋酸乙烯共聚物复合低热水泥浆体的水化.通过X射线衍射定性及定量分析测定了养护后样品的组成及水泥中硅酸三钙(3CaO·SiO2,C3S)、硅酸二钙(2CaO·SiO2,C2S)的水化率;利用带固体样品测试装置的全有机碳素分析仪测定了样品所吸收的CO2量;采用水银压入法检测了样品的孔径分布.结果显示:碳化养护大大促进了低热水泥的水化,并有球霰石生成.样品中的总孔隙体积也明显减少,但有大量较大孔径的毛细孔隙存在.碳化养护前,对样品进行水中预养护可以减少这些毛细孔隙,但不利于水泥的水化并导致CO2吸收量及抗折强度显著降低.     

Improved mechanical properties of NR/EPDM and NR/ butyl blends by precuring EPDM and butyl

Ethylene-propylene-diene rubber (EPDM) and isobutylene-isoprene rubber (IIR) were compounded, precured to a low degree, and then were blended with natural rubber (NR). The compounding ingredients for NR were then added and the final curing was done. NR/EPDM and NR/IIR blends, prepared using this method, were found to possess much improved mechanical properties as compared to their conventional counterparts. The optimum precuring crosslink density that has to be given to the EPDM and IIR phases has been determined. © 1993 John Wiley & Sons, Inc.     

Effect of rheological behavior of epoxy during precuring on foaming

In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 10²–10³ to 10⁶Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G′(ω) and G″(ω) decreased with increasing precuring time. Correspondingly, tan δ showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895–935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960–1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t < 1080 s) before foaming: large bubbles (>100 μm) and small ones (?30 μm). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

FE simulation of the curing behavior of the epoxy adhesive Hysol EA-9321

Cold-curing adhesives, characterized by an unsteady curing degree, present various advantages for assembling large scale structures set up under outdoor conditions. Thus various applications can be found in aerospace and automotive industries where structures are affected by thermal and mechanical loads. Hence, the curing state of the adhesive must be known to evaluate the lifetime of such bonded structures. The evolution of the polymerization of the adhesive Hysol EA-9321 during the curing process was examined in this paper. To that end, the curing degree of the adhesive was experimentally and analytically investigated for different curing cycles with a view to a potential application in the aerospace domain, where structures are assembled at low temperatures. Existing dynamic and isothermal curing models were applied to simulate the curing behavior of the adhesive. Then, an FEM model was developed to simulate the process of adhesive curing by taking into account a thermo-kinetic coupling.     

Geopolymeric materials prepared using Class F fly ash and elevated temperature curing

This paper reports the results of the study of the influence of elevated temperature curing on phase composition, microstructure and strength development in geopolymer materials prepared using Class F fly ash and sodium silicate and sodium hydroxide solutions. In particular, the effect of storage at room temperature before the application of heat on strength development and phase composition was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM were utilised in this study.Long precuring at room temperature before application of heat was beneficial for strength development in all studied materials, as strength comparable to 1 month of curing at elevated temperature can develop in this case only after 24 h of heat curing. The main product of reaction in the geopolymeric materials was amorphous alkali aluminosilicate gel. However, in the case of sodium hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1 (gismondine) zeolites and hydroxysodalite were also present. The type of zeolite present and composition of aluminosilicate gel were dependent on the curing history.     

光固化粉末涂料涂膜性能研究

以不饱和聚酯和丙烯酸环氧树脂为光固化粉末涂料的基体树脂,研究了两种基体树脂的结构、配比对光固化涂膜固化度及其性能的影响。结果表明固化度是影响耐溶剂性能、附着力、涂膜硬度和冲击强度的关键,适宜的n(UP)/n(EA)为1∶1;固化度应大于95%,可以达到99%。     

Drying and curing behaviour of melamine formaldehyde resin impregnated papers

Melamine formaldehyde (MF) resins are widely used for the gluing and surface coating of wood‐based consumer products in the interior design of living environments. MF resins are especially relevant in decorative laminate applications because of their good performance‐to‐price ratio. In their industrial processing, an important intermediate state is the liquid MF prepolymer that is used for decorative paper impregnation. Here, the drying of impregnated papers is investigated with respect to premature curing. A new method to quantify water release upon drying that allows estimation of the degree of undesired precuring is described. Since curing proceeds via polycondensation, crosslinking brings about the release of water molecules. By thermogravimetric analysis (TGA), drying was studied in terms of water release due to physical drying (elimination of “dilution water”) and chemical crosslinking of the prepolymer to a three‐dimensional MF network (elimination of chemically liberated water). The results obtained by TGA/IR spectroscopic analysis of the liberated volatiles show that the emission of water from b‐stage MF can be clearly analytically separated into a physical (evaporation of dilution water) and a chemical (liberation via condensation) sequence. TGA experiments were correlated with curing experiments performed with differential scanning calorimetry (DSC) to estimate the residual crosslinking capacities of the impregnated papers. The drying conditions used during the preparation of impregnated decorative papers seemed to significantly affect their remaining reactivity only when harsh drying conditions were used. Upon heat exposure for prolonged time, precuring of the oligomer units results in a shift of the temperature maxima in TGA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39860.     

Liquid-rubber-modified epoxy adhesives cured with dicyandiamide. I. Preparation and characterization

n-Butylacrylate/acrylic acid (nBA/AA) copolymers were synthesized and used to modify epoxy resin (DGEBA) cured with dicyandiamide (DICY). The precuring reaction between nBA/AA copolymer and DGEBA, the curing cycle of DGEBA, and the effects of DICY and aluminum powder upon the adhesive strengths of modified DGEBA were studied. It was found that the optimum DICY/DGEBA ratio was 6 g/100 g, and lap shear strength and T-peel strength increased with increasing amount of aluminum powder. The curing cycle for modified DGEBA was determined to be 1 h at 177°C.